1. Field of the Invention
The present invention generally relates to a photoconductive drum to be used in an electrophotographic image forming apparatus such as a copier, a printer, and a facsimile machine and an image forming apparatus having the photoconductive drum.
2. Description of the Related Art
A photoconductive drum having a cylindrical shape in an electrophotographic image forming apparatus is required to be replaced periodically because the surface of the photoconductive drum may be worn out and the electrical characteristics of the surface may be deteriorated in accordance with the number of printed pages and the like. Some types of photoconductive drums have a photoconductive sleeve member and a wheel member, the photoconductive sleeve member having a cylindrical shape and having an outer circumference surface on which a photoconductive layer is formed, the wheel member being provided for establishing the connection between the photoconductive sleeve member and the driving shaft of the main body of the image forming apparatus. There are generally two methods of replacing the photoconductive drum having the photoconductive sleeve member and the wheel member. One is to replace the entire photoconductive drum with the photoconductive sleeve member and the wheel member. The other method is to separate the photoconductive sleeve member from the wheel member with each other and replace the photoconductive sleeve member only so that the wheel member can be repeatedly used (reused). In comparison between those two method, the method of replacing the photoconductive sleeve member only may have some advantages including that a fewer number of parts may be required to be replaced in replacing the photoconductive drum and that the running cost of the image forming apparatus may be more reduced. Because of the advantages, from the viewpoint of the cost, the method of replacing the photoconductive sleeve member only has been more widely used as the method of replacing the photoconductive drum especially in the image forming apparatuses in which the printing speed is relatively high and a relatively large number of pages are to be printed during the service life. This is because the frequency of replacing the photoconductive drum is higher in such image forming apparatus.
However, in a case where the method of replacing the photoconductive sleeve member only is adopted, if an operator touches the surface of the used photoconductive sleeve member, the hand of the operator may be stained due to dirt on the surface. Furthermore, if the operator touches the surface of a new photoconductive sleeve member to be used, the stain on the hand of the operator may be adhered to the surface of the photoconductive sleeve member and/or the surface of the photoconductive sleeve member may be damaged, thereby degrading the image quality. Therefore, it is required to pay particular attention so as not to touch the surface of the photoconductive sleeve member during the replacement.
Because of the restriction that the operator cannot touch the surface of the photoconductive sleeve member, in the apparatus in which only the photoconductive sleeve member is to be replaced, it may take longer to complete the replacement of the photoconductive drum, thereby increasing the repair and maintenance cost. Some efforts have been made to overcome the problem.
For example, Japanese Patent Application Publication No. H02(1990)-502130 describes an image forming apparatus in which only the photoconductive sleeve member can be replaced without any necessity of touching the surface of the photoconductive sleeve member. FIGS. 1 and 2 show an example of the conventional photoconductive drum 100 of the image forming apparatus. As shown in the figures, the photoconductive sleeve member 1 is replaceable with respect to the apparatus main body. FIG. 1 is a cross-sectional view when cut along the center line of the conventional photoconductive drum 100. FIG. 2 is a cross-sectional view of the cross section perpendicular to the center line of the photoconductive drum 100. More specifically, FIG. 2 is the cross-sectional view of the cross section when cut along line A-A′ of FIG. 1; and FIG. 1 is the cross-sectional view of the cross section when cut along line B-B′ of FIG. 2.
Further, FIGS. 3A and 3B show a process of attaching and detaching the photoconductive sleeve member 1 of the photoconductive drum 100 to and from a driving shaft 4 of the apparatus main body.
As shown in FIGS. 1 and 2, the photoconductive drum 100 includes the photoconductive sleeve member 1 having a hollow cylindrical shape, a cap member 2, and a wheel member 3. The cap member 2 serves as a first end surface member capable of engaging with one end of the photoconductive sleeve member 1 in the center line direction. The wheel member 3 serves as a second end surface member capable of engaging with the other end of the of the photoconductive sleeve member 1 in the center line direction. The driving shaft 4 transmits drive torque the photoconductive drum 100 and is supported by shaft bearing members (not shown) of the image forming apparatus, the shaft bearing members being provided at both ends of the driving shaft 4 in the centerline direction. Further, the wheel member 3 is fixed to the driving shaft 4, and the cap member 2 and a handle 5 (FIG. 1) are removably attached to the driving shaft 4.
One end side of the cylindrical-shaped photoconductive sleeve member 1 is engaged with the outer circumference of the cap member 2 which is fixed to a small diameter part 4b of the driving shaft 4. On the other hand, the other end side of the cylindrical-shaped photoconductive sleeve member 1 is engaged with outer circumference of the wheel member 3 fixed to a stepping part 4c formed between the small diameter part 4b and a large diameter part 4a of the driving shaft 4. Further, by screwing the handle 5 into the end portion of the small diameter part 4b of the driving shaft 4, the photoconductive sleeve member 1 is sandwiched between a cap flange section 2f of the cap member 2 and a wheel flange section 3f of the wheel member 3. As a result, the photoconductive sleeve member 1 is fixed in position with respect to the driving shaft 4. Further, the wheel member 3 serves as a guide member capable of guiding the photoconductive sleeve member 1 when the photoconductive sleeve member 1 is attached to and detached from the main body of the image forming apparatus. To that end, the wheel member 3 includes plural ribs 30 extending along the inner circumferential surface of the photoconductive sleeve member 1.
Further, in the photoconductive sleeve member 1, there is provided a deformation prevention member 7 contacting plural portions arranged in the circumferential direction on the inner circumferential surface of the photoconductive sleeve member 1. As shown in FIG. 2, the deformation prevention member 7 includes a first prevention piece 71 and a second prevention piece 72. The first prevention piece 71 and the second prevention piece 72 are engaged with each other at an engaging section 70 having a concavo-convex shape, so that the first prevention piece 71 and the second prevention piece 72 can pivotably rotate about the engaging section 70 due to a pressing force generated by a strut spring 73. The strut spring 73 is provided in between the first prevention piece 71 and the second prevention piece 72. In the rotations, the first prevention piece 71 rotates in the arrow direction C1 and the second prevention piece 72 rotates in the arrow direction C2 in FIG. 2. By rotating in this way, the deformation prevention member 7 enlarges its circumferential dimension, thereby causing contacting sections (71b and 72b in FIG. 2) of the prevention piece 71 and the second prevention piece 72 to be in contact with the inner circumferential surface of the photoconductive sleeve member 1 to press the inner circumferential surface of the photoconductive sleeve member 1.
Further, the prevention piece 71 includes an engagement core 71a provided where the first prevention piece 71 and the second prevention piece 72 are pressed by the strut spring 73, so that the engagement core 71a can be entered into (moved through) an engage hole formed in the second prevention piece 72. Further, the strut spring 73 is disposed inside the engagement core 71a. Further, the second prevention piece 72 includes a fixing screw 72a to fix the position of the engagement core 71a. Therefore, by tightening the fixing screw 72a, it becomes possible to fix the position of the engagement core 71a with respect to the second prevention piece 72. By doing this, the positional relationship between the first prevention piece 71 and the second prevention piece 72 can be fixed (determined) regardless of the pressing force (status) of the strut spring 73. In this configuration, while the strut spring 73 is being compressed, by tightening the fixing screw 72a, the first prevention piece 71 and the second prevention piece 72 can no longer press the inner circumferential surface of the photoconductive sleeve member 1. In this situation, it becomes possible to remove the deformation prevention member 7 from inside the photoconductive sleeve member 1.
Next, a procedure of removing the photoconductive sleeve member 1 of the photoconductive drum 100 from the image forming apparatus and replacing the photoconductive sleeve member 1 is described.
To replace the photoconductive sleeve member 1, as shown in FIG. 3A, first, the handle 5 is removed from the driving shaft 4. Next, the cap member 2 is removed. When the cap member 2 is removed, an opening is formed on the left-hand side of the photoconductive sleeve member 1 as shown in FIG. 3A. Through the opening, by placing the hand of an operator in the photoconductive sleeve member 1, the operator can grasp the deformation prevention member 7. In this situation, the fixing screw 72a is not tightened. Therefore, due to the pressing force of the strut spring 73, the contacting sections (71b and 72b in FIG. 2) of the prevention piece 71 and the second prevention piece 72 are in contact with the inner circumferential surface of the photoconductive sleeve member 1 and pressing the inner circumferential surface. As a result, the deformation prevention member 7 is fixed in position with respect to the photoconductive sleeve member 1 so that the deformation prevention member 7 and the photoconductive sleeve member 1 are integrated with each other. In this situation, when the operator grasps the deformation prevention member 7 as a handle member and then pulls the deformation prevention member 7 to the left-hand side in FIG. 3A, the photoconductive sleeve member 1 can be removed from the driving shaft 4 and the wheel member 3. That is, the photoconductive sleeve member 1 can be removed from the main body of the image forming apparatus.
Then, the deformation prevention member 7 is removed from the inside of the photoconductive sleeve member 1. Next, a new photoconductive sleeve member 1 is attached to the deformation prevention member 7. Then, by fixing the photoconductive sleeve member 1 with the deformation prevention member 7 to the driving shaft 4 in the procedure opposite to that of removing the photoconductive sleeve member 1 described above, the replacement of the photoconductive sleeve member 1 can be completed.
In the above method, it is true that only the photoconductive sleeve member 1 may be replaced and the deformation prevention member 7 as the handle member may be reused. However, the operation of removing the handle member disposed in the photoconductive sleeve member 1 may be so difficult that it may increase time to complete the replacement of the photoconductive sleeve member 1.
On the other hand, there may be another method in which an operator can grasp the handle member disposed in the photoconductive sleeve member to replace the photoconductive sleeve member so that the entire photoconductive sleeve member including handle member may be replaced (i.e., the handle member cannot be reused). However, from the viewpoint of saving resources, discarding the handle member in this method is a waste of resources.
Japanese Patent Application Publication No. 2008-203425 discloses a configuration including an engagement unit capable of switching between an engagement state and a non-engagement state based on the operation of an operation member. In the engagement state, an end surface member corresponding to the cap member 2 of the photoconductive drum 100 shown in FIGS. 1 through 3B is engaged with the photoconductive sleeve member. On the other hand, in the non-engagement state, the engagement between the end surface member and the photoconductive sleeve member is released. The engagement unit is provided in one of the end surface members. The engagement unit includes a sleeve inner circumferential surface pressing member. By operating the operation member, it becomes possible to switch between the engagement state and the non-engagement state. In the engagement state, the sleeve inner circumferential surface pressing member is in contact with the sleeve inner circumferential surface (i.e., the inner circumferential surface of the photoconductive sleeve member) to press the sleeve inner circumferential surface. On the other hand, in the non-engagement state, the sleeve inner circumferential surface pressing member is not in contact with the sleeve inner circumferential surface. While the sleeve inner circumferential surface pressing member is not in contact with the sleeve inner circumferential surface, the engagement between the end surface member and the photoconductive sleeve member is released. From this state where the engagement is released, by operating the operation member, the sleeve inner circumferential surface pressing member comes in contact with the sleeve inner circumferential surface to press the sleeve inner circumferential surface. By doing this, the end surface member comes in contact with the sleeve inner circumferential surface. According to the configuration described in Japanese Patent Application Publication No. 2008-203425, when the photoconductive sleeve member is to be replaced, an operator operates the operation member to engage the end surface member with the photoconductive sleeve member. Then, the operator pulls the end surface member engaged with the photoconductive sleeve member in the center line direction to integrally remove the end surface member and the photoconductive sleeve member from the other end surface member and the driving shaft. Then, the operator operates the operation member to release the engagement between the end surface member and the photoconductive sleeve member to separate the end surface member from the photoconductive sleeve member, the end surface member having been engaged with the photoconductive sleeve member and integrally removed from the driving shaft as described above. By doing this, it becomes possible to replace only the photoconductive sleeve member.
By having this configuration, the end surface member engaged with the photoconductive sleeve member and integrally removed from the driving shaft may serve as a handle member; therefore, the operator doesn't have to place a hand inside the photoconductive sleeve member to remove the handle member from the photoconductive sleeve member. As a result, it becomes possible to easily separate the handle member from the photoconductive sleeve member, and it may not increase time to complete the replacement of the photoconductive sleeve member. Further, the end surface member serving as the handle member may be reused by being engaged with a new photoconductive sleeve member. Therefore, it is not necessary to discard the end surface member, which is useful from the viewpoint of saving resources.
Further, according to the configuration described in Japanese Patent Application Publication No. 2008-203425, one end surface member engaged with the photoconductive sleeve member can be integrally removed from the other end surface member and the driving shaft. However, as an alternative configuration, two end surface members and the photoconductive sleeve member may be removed from the driving shaft. Then, one end surface member and the photoconductive sleeve member may be integrally removed from the other end surface member. In this configuration, for example, while a hand or a tool is used to serve as the separated driving shaft to fix the position of the other end surface member, by removing the end surface member from the other end surface member, it becomes possible to integrally remove the end surface member and the photoconductive sleeve member from the other end surface member.
However, in the configuration described in Japanese Patent Application Publication No. 2008-203425, the one end surface member is engaged with the photoconductive sleeve member based on a friction force exerted between the sleeve inner circumferential surface pressing member and the sleeve inner circumferential surface. Therefore, a retention force retaining the position of the photoconductive sleeve member with respect to the one end surface member by the sleeve inner circumferential surface pressing member is constant. Therefore, because of such a strong engagement between the photoconductive sleeve member and the other end surface member, when an operator integrally removes the one end surface member and the photoconductive sleeve member from the other end surface member, more force than is supposed by the design engineer may be temporarily applied to the contacting section between the sleeve inner circumferential surface pressing member and the sleeve inner circumferential surface. In this case, if the applied force exceeds the maximum static friction force between the sleeve inner circumferential surface pressing member and the sleeve inner circumferential surface, the engagement between the one end surface member and the photoconductive sleeve member may be destroyed (released). When the engagement is destroyed, the engagement between the photoconductive sleeve member and the other end surface member may not be released, thereby preventing the replacement of the photoconductive sleeve member only. Further, when, for example, an operator holds the other end surface member, and if the engagement is destroyed, the photoconductive sleeve member may be dropped off and the operator may be injured.
To avoid the problems, a new configuration may be adopted in which a biasing member such as a spring member having a higher biasing force is provided to increase the pressing force of the sleeve inner circumferential surface pressing member with respect to the sleeve inner circumferential surface. However, in a case where this method is adopted to increase the biasing force of the biasing member, while the end surface member is in contact with the photoconductive sleeve member, the higher pressing force is always applied to the contacting section between the sleeve inner circumferential surface pressing member and the sleeve inner circumferential surface including when such higher pressing force is not required. Because of this feature, it may become necessary to reinforce the members so as not to be deformed even when the higher pressing force is applied to the contacting section between the sleeve inner circumferential surface pressing member and the sleeve inner circumferential surface, thereby increasing the manufacturing costs.